1. Field of the Invention
The present invention relates to a wheel support structure of a motorcycle (two-wheeled motor vehicle) such as a standard motorcycle, scooter and the like, and more particularly to a wheel support structure for a motorcycle having a wheel rotational speed detection apparatus.
2. Description of the Related Art
Anti-lock brake systems (ABS) are widely used as a device for stabilizing the traveling state of an automobile. Use of such an ABS has mainly been centered on four-wheeled motor vehicles, however, in recent years, such systems have begun to be used in two-wheeled motor vehicles as well. As is well known, in order for ABS control it is necessary to find the rotational speed of the wheels, so conventionally installing a rotational speed detection device in a wheel-supporting ball bearing unit for allowing a wheel to be supported by the suspension such that the wheel rotates freely is widely performed.
However, construction of a rotational speed detection apparatus for a four-wheeled motor vehicle cannot be used as is in an apparatus for a two-wheeled motor vehicle. The main two reasons for this are that (1) a wheel-supporting ball bearing for a two-wheeled motor vehicle is rather compact when compared with a wheel-supporting ball bearing for a four-wheeled motor vehicle, and (2) whereas many wheel-supporting ball bearings for four-wheeled motor vehicles are inner ring rotating type, many of the wheel-supporting ball bearings for two-wheeled motor vehicles are outer ring rotating type, and for that reason the construction of a rotational speed detection device for a four-wheeled motor vehicle cannot be applied as for use in a two-wheeled motor vehicle.
FIG. 35 illustrates an example of construction for supporting a wheel of a motorcycle, and illustrates the construction of the portion that supports the wheel of a relatively compact motorcycle such as a scooter or the like such that the wheel can rotate freely. This wheel support apparatus 1 for a motorcycle comprises a pair of single-row ball bearings 4, a support shaft 3 that is fits inside the inner rings of these ball bearings 4, with both end sections thereof fastened to the vehicle body by way of a pair of forks 2, and a hub 6 that supports the tire by way of a wheel 7 such that the tire can rotate freely. In this construction, inner ring spacers 5a, 5c are mounted between the inner rings of the ball bearings and the forks 2, and an inner ring spacer 5b is mounted between the inner rings of the ball bearings 4, so that even when the support shaft 3 is tightly fastened on both ends by a nut 8, there is no large axial load applied to these ball bearings 4.
On the other hand, a rotational speed detection apparatus that uses a rolling bearing with magnetic encoder such as disclosed in JP2007-321894(A), JP2006-105341(A), JP2007-139075(A), JP2007-211840(A), JP2007-285514(A) and JP2009-229157(A) has been conventionally known as a rotational speed detection apparatus to be installed for controlling the ABS of a motorcycle. FIG. 36 illustrates an example of a ball bearing with a magnetic encoder as disclosed in JP2007-3321894(A). This ball bearing 10 with magnetic encoder comprises: an outer ring 11, which is the rotating ring; an inner ring 12, which is the stationary ring; a plurality of balls 13, which are rolling bodies that are located between the outer ring 11 and the inner ring 10 such that they can roll freely; a retainer 14 that holds the balls 13 such that they are uniformly space and such that they can roll freely; a sealing plate 15 that is attached to one of the end sections in the axial direction of the outer ring 11 and comes in sliding contact with the inner ring 12; and a sealing plate 16 with a magnetic encoder that is attached to the other end in the axial direction of the outer ring 11 and that comes in sliding contact with the inner ring, the magnetic encoder 9 being mounted on and fastened to the outside in the axial direction of this sealing plate 16.
By installing this kind of ball bearing 10 with magnetic encoder in the place of one of the pair of single-row ball bearings 4 that are assembled in the construction illustrated in FIG. 35, and by detecting the rotational speed of the magnetic encoder 9 of the ball bearing 10 with magnetic encoder by way of a magnetic sensor 17, it is possible to detect the rotational speed of the wheel 7, or in other words, it is possible to detect the rotational speed of the wheel of the motorcycle. FIG. 37 illustrates an example of construction of a wheel support apparatus for a motorcycle comprising this kind of magnetic encoder. In this construction la, a magnetic sensor 17 is fastened to the non-rotating inner ring spacer 5a so that the magnetic detection surface thereof faces the detected surface of the magnetic encoder of the ball bearing with magnetic encoder. The output from the magnetic sensor 17 is transmitted to an external computing device (not illustrated in the figure) by way of a harness 19, and is appropriately used for brake control by the ABS apparatus. In addition to the example illustrated in FIG. 37, FIG. 38 illustrates construction of another example of a rotational speed detection apparatus wherein a ball bearing 10 with magnetic encoder and circular ring-shaped holder member 18 are arranged on the support shaft 3 and the magnetic encoder 9 closely faces the magnetic sensor 17 that is supported by the holder member 18.
As described above, this kind of wheel-supporting rolling bearing for a two-wheeled motor vehicle is more compact than a wheel-supporting rolling bearing for a four-wheeled motor vehicle, and the size of the magnetic encoder that can be used is limited. Therefore, the magnetic flux density per magnetic pole of a magnetic encoder for a two-wheeled motor vehicle is smaller than in a magnetic encoder for a four-wheeled motor vehicle, so in order to detect rotational speed with good precision in a rolling bearing with rotational speed detection apparatus for a motorcycle, there is a problem in that either the ease of assembly must be sacrificed in order to reduce the air gap space between the sensor and the magnetic encoder, or the resolution must be sacrificed in order to reduce the number of magnetic poles in the circumferential direction of the magnetic encoder. However, when the component elements of the rolling bearing elastically deform due to a moment that is applied during operation, the possibility that rubbing will occur between the detection part of the magnetic sensor and the detected surface of the encoder becomes high, so in that case reducing the air gap is not preferable. Moreover, when the number of magnetic poles is reduced, the number of times that rotational speed detection can be performed during one rotation of the wheel is reduced, so is disadvantageous from the aspect of maintaining speed of ABS control.
In the case of a rotational speed detection apparatus for the wheel of a two-wheeled motor vehicle, differing from an apparatus for a four-wheeled motor vehicle, the magnetic encoder 9 is supported by and fastened to the hub 6 by way of the outer ring 4 instead of being fastened directly. Therefore, when there is slippage in the fit between the hub 6 and the outer ring 4, and so-called creep occurs, there is a problem in that the rotational speeds of these members do not match, and reliability of the rotational speed detection of the wheel is lost. Construction for preventing the occurrence of this kind of creep such as that disclosed in JP10-82428(A), JP2001-27255(A), JP2005-33999(A), JP09-314695(A), JP2003-287043(A) and JP2007-315585(A) has been known, however, up until now, using construction for preventing the occurrence of this kind of creep in order to improve the reliability of the rotational speed detection in a motorcycle has not been investigated.
Furthermore, the sealing plate with magnetic encoder in this kind of rolling bearing with rotational speed detection apparatus comprises a metal core, seal lips and a magnetic encoder, however, because the both the seal lips and the magnetic encoder cannot be mounted and fastened to the metal core in a single process, processing becomes complex, and processing requires time. Such a problem makes it difficult to lower the costs of the wheel support apparatus for a motorcycle that uses this kind of rolling bearing with rotational speed detection apparatus.